Its power and toughness grow with every card in your opponents graveyards, and every spell you cast feeds it more
The goal of this deck is to cast a ton of creatures, flooding the board with humans, then leverage our powerful Humans and +1/+1 Counter synergies to grind out value, pump our team, and swing for lethal
That doesn't stop all things from happening to you like a Teferis Protection might (and even then, there are ways around that too), but it does stop you from being targeted directly by everything from cards to attacks to Planeswalker abilities
This has been reprinted a number of times, but its original Urzas Legacy printing retains a certain cachet, what with the cozy atmosphere of the art from Scott M
In contrast, you pretty much can't go wrong playing exactly 60 cards in your Constructed deck, or 40 cards in your Limited deck
The ulti is sufficiently good that it gets a lot of concessions a couple of turns ahead of it being an option